1. Field of the Invention
This invention relates to the separation of minerals, in particular to a process for the separation of the minerals copper, iron and gangue contained in a concentrate, from the molybdenite contained in the concentrate.
2. Description of the Prior Art
The process of the invention comprises the separation of minerals and gangue which creates an ore, through the process known as flotation. To carry out the separation, chemical substances are used in the system in order to control the behavior of the individual minerals in accordance with the kinetics of flotation.
Ground ore is processed with water to form pulp. The surfaces of the mineral particles are treated with specific chemical reagents that induce hydrophobic or hydrophilic characteristics in the different components of the ore, depending on the properties of such different components.
In a flotation cell, air bubbles are produced, e.g., by agitation of the pulp or by the introduction of pressurized air, and the air bubbles come to the surface. During their ascent they encounter the ore particles in the pulp. Chemical reagents which produce foam may also be added to produce these bubbles and stabilize the foam.
The surfaces of the minerals with hydrophobic characteristics will adhere to the bubbles at the air-liquid interface. In this way, the mineral is carried towards the top of the flotation cell to a level where the pulp overflows in the form of a foam.
Certain of the minerals in the pulp may not be wanted in the process or may not be wanted in this phase of it; and for this reason, chemical reagents must be used to control the recovery sequence of the undesirable minerals. In order to depress the tendency of the unwanted minerals to float, a hydrophilic environment must be established so that the undesirable minerals are wetted and, thus, do not adhere to the air bubbles.
This environment is created by inhibiting adsorption of the collecting reagent and foaming reagent on the surfaces of the undesirable mineral or minerals; that is, by increasing their hydrophilic characteristics. In order to be effective, this phase must be selective accentuating the hydrophobicity of the minerals which it is desired to float, after adding the proper doses of collector reagents.
Recuperation and depression of the minerals is not complete, and there will always be fractions of undesirable minerals mixed with the desirable ones, and vice versa. Avoiding this overlapping of desirable with undesirable minerals contributes, among other factors, to a more economical process of concentration by flotation.
The floating of the minerals by means of foam depends entirely on the surface phenomenon which develops on the facets of the metallic or non-metallic minerals contained in an ore. Only a small surface of the particles is required for the adherence of a substance in the formation of a compound on the facet of the crystal of the mineral. When there are completely cleaned surfaces, the adhesion is complete and the particle floats easily. Interferences with a good adherence are caused by various pulp components, but the most common and the one that affects proper flotation the most is the component of the ore commonly known as ore dust; that is, fine particles usually of less than 70 microns in size.
Separation of the molybdenite from a concentrate of copper minerals involves complicated chemical processes for treating the particles with depressors which inhibit copper floating and improve floating of the molybdenite. The pulp is stirred for a period of 24 to 48 hours, and it is washed with live steam. The processes of concentrate roasting and oxidation are used, together with the decant of fine particles, as well as various combinations of these processes.
The depression of the copper minerals, or the depression of the molybdenite, when applicable, requires conditioning with toxic and dangerous chemicals, as well as the use of inconvenient chemical products. Such materials include arsenic trixoide, phosphorous pentasulfide, sodium cyanide, sodium hydrosulfide, ammonium sulfide, and others. The roasting step, as well as the re-milling of the calcined product, are normally in the intermediate stage of the process.
Many cleaning steps by floating are required in order to produce the desired standard of concentrate; however, value is lost in each step. It is also strictly necessary to supervise the disposal of the residual toxic substances from these complicated processes. This and other factors increase operating costs.
The flotation process may also be conducted in reverse by depressing the molybdenite with the addition of a dextrine solution to the pulp. The copper and iron sulfides are floated and the molybdenite is depressed. In this process, it is necessary to treat the dextrine before trying to thereafter clean the molybdenite by floating.
The minerals which float by themselves, such as talc, sulfur and carbon, are mechanically separated through classification in hydrocyclones, or otherwise with some treatment before the next floating stage.
It is an object of this invention to provide a process for separation by flotation whereby copper, iron and gangue minerals contained in a concentrate are separated from the molybdenite contained in the concentrate, through the use of a system of simple reagents and of reduced toxicity.
Another object of the invention consists in providing a process which achieves excellent depression of undesirable minerals and gangue and a very efficient recuperation of molybdenite.
It is an object of the invention, in contrast to complex prior art systems which use many chemical substances, to provide a process based on a simple system for flotation in which, through the use of appropriate reagents, a maximum depression is obtained, above 90%, of the minerals gangue which are not wanted. Molybdenite particles are produced simultaneously which have a great tendency to float significantly increasing recuperation of the desired mineral.